AnsweredAssumed Answered

Factor of Safety (ply 1) w/ Composite

Question asked by Max P on Mar 25, 2012

I'm trying to design a multi-ply composite pressure vessel, just as a learning exercise.


When I run the simulation I'm getting a von Misen Stress result (-Ply 1-) that is very slightly below the yield strength of the composite that is actually making up Ply 1.   The von Misen Stress result for all plies (-Max-) is just a tiny bit higher than the yield strength.


My gut tells me that this indicates likely first-ply-failure.   Can anyone confirm that assumption for me?


When I then bring up a Max Normal Stress Factor of Safety distribution result [note: it is clearly marked: (-Ply 1-) ], I'm getting a *very* high FOS figure well above 20,000!   That number is very difficult to believe, given the poor von Misen results.


So, I'm guessing that either the FOS is actually reporting the condition of the complete multi-ply structure and is just mistakenly calling it Ply 1, or perhaps the von Misen Stress chart is actualy showing the stresses on an unsupported Ply 1 and the FOS is then showing how Ply 1 behaves when it *is* supported by all the other Ply's, hence the disparity.


Can someone please provide some insight into what I'm seeing here?   Should I put any faith in that FOS figure (could save a lot of weight!), or should I re-design to exceed the Ply 1 von Mises strength by a comfortable margin?




PS - I only have SW2011 Premium and I don't have (and can't afford) Simulation Premium, so I can't run Tsai-Hill or Tsai-Wu